I guess the problem here is counterparty risk. If the solar farm goes bankrupt, you lost your investment. Also they may be illiquid (hard to sell?).

That is probably why you are investing your bonus, rather than selling everything to go all in. Because apart from the counterparty risk, 15% lifetime yield is pretty good. Obviously there is a threat from unlimited energy scenario like cold fusion, but that is probably 35 years away :-).